In the general case, you normally can't expect to go to your favorite game shop, pick up a PC game, take it home, and expect to be able to put the game on your Mac and have it run. However, it is possible to play PC games on a Mac. When attempting to play a Windows game on a Mac OS-based machine, you have several options, each with its drawbacks and strengths.

Please note: This is intended as general advice to a non-technical audience. This is not indented to be a "catch-all" answer to "how do I overcome game X's difficulties when running under solution Y." The existence of this answer does not mark every other MacOS gaming question on this topic as a duplicate. It is further not meant to be a full and complete overview of WINE/Virtual Machines/dual booting/etc. The intent is to generally summarize the solutions to allow people to choose a direction to invest further effort.

Get the Mac Port

If it exists, getting the Mac port or playing it natively on your Mac is almost always the best way to play any game on a Mac. With the advent of things like SteamPlay and the rise of independent game houses, more and more games are coming out for the Mac. Don't assume that the game is Windows-only until you've done the research. More and more games are now showing up in browsers, which can also sometimes make them platform independent. Whenever you can, invest time in researching the Mac version of a game, as playing it typically produces the best experience.

Pros

• Support Mac publishers and encourage more Mac games.
• Usually the best possible experience, designed for your OS.
• Better support for 3D acceleration and other advanced hardware features.
• Some features that you want may be platform-specific and only available on Mac.

Cons

• Not all games have a Mac port.
• Sometimes can be expensive to re-purchase a game if you already own it.
• Some features that you want may be platform-specific and unavailable on Mac.
• Sometimes the Mac port is bad, or is actually a version of the game ported using one of these other methods (see Emulation).

Virtual Machine

With desktop virtual machine software, you can run a copy of Windows as a "program" under Mac OS. Several software packages exist, such as VirtualBox, Parallels, and VMWare Fusion. Once you've installed the virtual machine software, you can follow a simple wizard to create a file on your hard drive to hold your Windows installation and applications, and then the system will walk you through setting up Windows from the install media.

Pros

• Setup is generally fairly easy - if you can install OSX programs and Windows programs, you can probably install a Windows virtual machine with little trouble.
• Integration with your existing OSX applications tends to be fairly seamless.
• Run a wide array of Windows apps without having to do any sort of complicated setup per-app.

Cons

• VM software is a resource hog, and will eat large chunks of your RAM, CPU, and disk space.
• The guest operating system (in this case, Windows) won't have full access to your hardware, so performance is going to be poorer than some of the other solutions on this list.
• 3D support and performance are generally fairly poor compared to the Mac Port or Dual Boot approaches, although this area is evolving.
• Cost - you need to own a license to Windows, and in most cases you will also have to purchase a license to the virtual machine software.

Dual Boot

With Apple's BootCamp software, you can install Windows into a separate part of your Mac's hard drive, and then you can choose to start either Windows or Mac OS on your Mac when you start it up. Apple provides technical manuals for properly installing BootCamp on your Mac, which are easy to follow and thorough.

Pros

• Windows is actually running on your hardware, so installing/playing Windows games is generally a breeze. Install them on your Mac just like you would on any other Windows PC.
• Windows has full control of your hardware, so 3D support and game performance are as good as comparable non-Mac hardware.

Cons

• Rebooting to switch between Mac OS and Windows is painful and time consuming.
• Requires that you have a valid, licensed copy of Windows, which can be expensive.

Emulation

Virtual machines emulate an entire PC, but oftentimes this solution is overkill. Emulators (and similar programs) only fake part of the device or OS in question, which can yield better performance with less overhead. Many different types/classes of emulators exist that emulate a wide variety of platforms and systems, for example:

• Darwine and CrossoverGames are based on the WINE project which attempts to reproduce Windows API calls on Linux/Mac.
• DOSBox emulates a DOS environment for older games.
• XNA games (such as Terraria) can be played on OSX via MonoGame.
• Console versions of games can be played on Macs with the appropriate console emulator, of which there are too many to list.

Pros

• Many emulators are free, and do not require a Windows license/install disc.
• Emulators generally require fewer resources than a virtual machine.

Cons

• Emulation can produce unstable results.
• Not all games are compatible with emulation.
• Emulators generally have poor support compared to other solutions - expect to experiment and invest time to get your game running properly.

Cloud Gaming

A fairly recent development is "cloud gaming" where the game's video is "streamed" to your computer in a fashion similar to how Netflix works, as opposed to your computer's OS and hardware rendering the video data locally. OnLive, one prominent player in this space, offers a wide library of games to choose from and supports playing games on most modern Macs.

Pros

• Larger library of games than traditionally offered as Mac ports
• Compatible with a wider array of hardware than other solutions (ie, Intel integrated graphics Macs aren't limited by what runs on an Intel chipset)

Cons

• Requires a constant, high-speed broadband connection in order to play.
• Pricing structure may not be appealing.
• Game selection may not be as broad as the selection under "Dual Boot" or "Virtual Machine" solutions.

Traditionally id games are all OpenGL based, so I would look at updating your Mac video card drivers for better / more mature OpenGL support.

If there aren't any graphic driver updates available for the Mac, you might be out of luck -- I don't think Nvidia or AMD/ATI offer independent (direct from their website, not through Apple) driver updates. At least there is no "Mac" OS selection at http://support.amd.com/us/gpudownload/Pages/index.aspx for example.